package club.jdiy.utils;

import lombok.extern.slf4j.Slf4j;

/**
 * <p>名称：IdWorker.java</p>
 * <p>描述：分布式自增长ID</p>
 * <pre>
 *     Twitter的 Snowflake(雪花算法)　JAVA实现方案
 * </pre>
 * 核心代码为其IdWorker这个类实现，其原理结构如下，我分别用一个0表示一位，用—分割开部分的作用：
 * 1||0---0000000000 0000000000 0000000000 0000000000 0 --- 00000 ---00000 ---000000000000
 * 在上面的字符串中，第一位为未使用（实际上也可作为long的符号位），接下来的41位为毫秒级时间，
 * 然后5位datacenter标识位，5位机器ID（并不算标识符，实际是为线程标识），
 * 然后12位该毫秒内的当前毫秒内的计数，加起来刚好64位，为一个Long型。
 * 这样的好处是，整体上按照时间自增排序，并且整个分布式系统内不会产生ID碰撞（由datacenter和机器ID作区分），
 * 并且效率较高，经测试，snowflake每秒能够产生26万ID左右，完全满足需要。
 * <p>
 * 64位ID (42(毫秒)+5(机器ID)+5(业务编码)+12(重复累加))
 *
 * @author ziquee(子秋) QQ号:39886616 主页: http://www.jdiy.club
 * @version 20200517
 */
@Slf4j
public class IdWorker {
    private static final IdWorker idWorker;

    static {
        idWorker = new IdWorker(0, 0);
    }

    public static long getId() {
        return idWorker.nextId();
    }

    private final long workerId;
    private final long datacenterId;
    private long sequence = 0L;
    // 时间起始标记点，作为基准，一般取系统的最近时间（一旦确定不能变动）
    private final long twepoch = 1587160165800L;
    private final static long workerIdBits = 5L;
    private final static long datacenterIdBits = 5L;
    private final long sequenceBits = 12L;
    private final long timestampLeftShift = sequenceBits + workerIdBits + datacenterIdBits;
    private long lastTimestamp = -1L;

    public IdWorker(long workerId, long datacenterId) {
        // sanity check for workerId
        long maxWorkerId = ~(-1L << workerIdBits);
        if (workerId > maxWorkerId || workerId < 0) {
            throw new IllegalArgumentException(
                    String.format("worker Id can't be greater than %d or less than 0", maxWorkerId));
        }
        long maxDatacenterId = ~(-1L << datacenterIdBits);
        if (datacenterId > maxDatacenterId || datacenterId < 0) {
            throw new IllegalArgumentException(
                    String.format("datacenter Id can't be greater than %d or less than 0", maxDatacenterId));
        }
        this.workerId = workerId;
        this.datacenterId = datacenterId;
        log.info(String.format(
                "worker starting. timestamp left shift %d, datacenter id bits %d, worker id bits %d, sequence bits %d, workerid %d",
                timestampLeftShift, datacenterIdBits, workerIdBits, sequenceBits, workerId));
    }

    public synchronized long nextId() {
        long timestamp = timeGen();

        if (timestamp < lastTimestamp) {
            log.error(String.format("clock is moving backwards.  Rejecting requests until %d.", lastTimestamp));
            throw new RuntimeException(String.format(
                    "Clock moved backwards.  Refusing to generate id for %d milliseconds", lastTimestamp - timestamp));
        }

        if (lastTimestamp == timestamp) {
            long sequenceMask = ~(-1L << sequenceBits);
            sequence = (sequence + 1) & sequenceMask;
            if (sequence == 0) {
                timestamp = tilNextMillis(lastTimestamp);
            }
        } else {
            sequence = 0L;
        }

        lastTimestamp = timestamp;

        long datacenterIdShift = sequenceBits + workerIdBits;
        return ((timestamp - twepoch) << timestampLeftShift) | (datacenterId << datacenterIdShift)
                | (workerId << sequenceBits) | sequence;
    }

    protected long tilNextMillis(long lastTimestamp) {
        long timestamp = timeGen();
        while (timestamp <= lastTimestamp) {
            timestamp = timeGen();
        }
        return timestamp;
    }

    protected long timeGen() {
        return System.currentTimeMillis();
    }
}
